Combination plug and receptacle



April 9, 1957 c. A. T. WlLDE COMBINATION PLUG AND RECEPTACLE Filed Feb. 23, 1956 ATTORNEY Unite States Patent 2,788,404 COMBINATION PLUG AND RECEPTACLE Charles A. T. Wilde, Toronto, Ontario, Canada, assignor to D. M. Fraser Limited, Toronto, Ontario, Canada Application February23, 1955, erial No. 567,380 3 Claims. (Cl. 200-51118) This invention relates to the electrical industry, and more particularly to an improved male plug, female receptacle, and circuit breaker for such industry.

There are many applications in the electrical field wherein a lamp or group of lamps or other electrical equipment is connected to a plug which is adapted to be inserted into a receptacle to complete an electrical circuit. Examples are in the lighting control field for stage, theatre and television studios wherein a single lamp or a group of lamps is connected to such a plug, and insertion of one or more such plugs into receptacles produces the required lighting efiects. When the electrical load connected with the plug is comparatively high it is important that the plug be inserted only into a dead receptacle, i. e. one which at the time of insertion is not electrically energized. After the plug is in inserted position, the circuit may then be completed by actuating a switch or circuit breaker.

The insertion of a plug attached to a heavy load into or withdrawal from a live receptacle causes arcing and burning of the contact points and materially shortens the life of the plug.

Since those using such devices are not infallible, it is desirable that some arrangement of plug, receptacle and circuit breaker be provided whereby the plug may not be inserted into the receptacle unless the circuit breaker controlling the supply of electricity to the receptacle is in the off position.

In addition, it is desirable to ensure that no overloading of a given circuit take place through insertion of a plug connected to a load greater than the capacity of the receptacle and associated equipment into which the plug is placed. It is not uncommon to have equipments of varying maximum capacity and even a limited form of overload protection would be most desirable.

It is a principal object of this invention, therefore, to provide a plug, receptacle and circuit breaker combina tion as will permit the plug to be inserted into and withdrawn from the receptacle only when the circuit breaker is in the off position.

It is a further important object of this invention to provide such a combination as will afford a limited form of overload protection.

It is another object of this invention to provide such a combination as will prolong the life of plugs and receptacles.

It is yet another object of this invention to provide such a combination as will afford ready visibility and unobstructed operation of the circuit breaker after insertion of the plug.

These and other advantageous objects will become ap' parent through a consideration of the following detailed description, taken in conjunction with the attached drawings in which Figure 1 is an end view of the plug which forms a portion of my invention;

Figure 2 is a vertical cross-section taken along line ice 2 2-2 of Figure 1 through the plug when fully inserted into the receptacle;

Figure 3 is a front view of the receptacle and circuit breaker mounting which forms a portion of this invention;

Figure 4 is a side view partly in section showing an attempt being made to insert the plug into the receptacle when the switch is in the on position;

Figure 5 is a view similar to Figure 4, but showing the plug being inserted when the switch is in the off position, and

Figure 6 is a front view showing the plug fully inserted and locked into position in the receptacle.

The invention consists broadly in the provision of a projecting, two position (on-off) circuit breaker mounted in proximity to anelectrical receptacle, together with a keyed plug adapted to be inserted in the receptacle, said plug having a bearing plate extending beyond the circuit breaker when the plug is so inserted and having a cutout portion so dimensioned and positioned that the plug may be fully inserted only when the circuit breaker is in the off position, but so that after insertion and completion of contact between plug and receptacle, the circuit breaker may be switched on or off as desired.

In greater detail and referring to the drawings which illustrate a preferred embodiment of the invention, the

invention comprises three main components, namely, a-

plug 1 adapted to be connected (via screw 4) to an electrical load; a receptacle 2 adapted to receive the plug and connected to a source of electrical power and a circuit breaker 3 mounted in proximity to the plug, the toggle of which projects beyond the plane of the receptacle mouth.

The plug shank is keyed towards its outer extremity in the form of a small projecting lug 5. The plug is provided with a non-conducting casing 6 to provide a handling portion, this casing terminating at the plug end in a bearing face 7. This bearing face has a. cut-out portion 8 in one quadrant thereof functioning in a manner which will be described in detail hereinafter.

The receptacle 2 is provided with a keyway 9 extending the length thereof and a boss 11 at the inner extremity of the receptacle. The keyway is adapted to receive the lug 5 and guide the plug into the receptacle in one position only. After the lug 5 has passed the boss 11, the whole pin may be rotated clockwise as viewed in Figures 1 and 5, one face of the lug 5 then being caused to bear against the boss 11, to prevent withdrawal of the pin after such rotation, and the degree of rotation of the plug being limited to the required amount by the dimensions of the chamber 10 into which it is permitted to rotate.

When thus inserted and rotated, the plug and receptacle are in positive and close electrical contact, and the plug cannot be withdrawn without a counter-clockwise rotation relative to the receptacle.

The circuit breaker 3 may be of the conventional off-on switch style illustrated in the drawings. It is mounted in proximity to the receptacle and in such a manner that the toggle 3A projects beyond the plane of the receptacle mouth. As shown in the drawings, the breaker is off when down, on when up, and is of the type which trips the circuit upon overload, then occupying a mid-position.

The operation of the various components is as follows:

All the lamps in a stage theatre or television studio will be connected in groups as desired, which are in turn connected to a male plug of the type described. These male plugs may conveniently be placed in a rack beneath a series of female receptacles and circuit breaker combinations as described above.

As required, one or another of the plugs may be inserted into a receptacle to supply electric current to the group of lights connected to such plug.

The key on the plug 1 and corresponding keyway 9 in the receptacle 2 ensure that the plug may be inserted in only one position. The cut-out portion 8 of the bearing face 7 is so arranged that when the plug is inserted, the toggle of the circuit breaker will bear against the bearing face of the plug and prevent complete insertion unless the toggle is in the off position, in which event, the cut-out portion of the face plate coincides with the position of the switch and permits complete insertion of the plug.

Figure 4 shows the relative position of receptacle, plug and circuit breaker when the switch is on and an attempt is made to insert the plug. It will be appreciated that the electrical circuit is completed only if the plug is fully inserted and that in the position shown in Figure 4, arcing or burning of contact points cannot take place.

If the toggle is in the off position (down as viewed in the drawings), however, the cut-out portion is such that the plug may be fully inserted as shown in Figure 5.

After the plug has been fully inserted, it must be given a slight clockwise rotation to lock it in the receptacle and to bring it in more positive contact with the receptacle contacts. The dimensions of the cut-out portion 8 are such that such rotation (which is limited by the dimensions of the chamber within which the lug 5 is permitted to rotate) is permitted without interference by the bearing face 7 of the circuit breaker toggle 3A. In its inserted and locked position the parts assume the relationship shown in Figure 6 where it will be observed that the toggle 3A may be actuated from off to on without hindrance from the bearing face 7.

The plug cannot be withdrawn however, without the counter-clockwise rotation required to align the lug 5 with the keyway 9 and when this rotation takes place the toggle is moved to the off position, thereby opening the circuit before withdrawal.

In practice, after insertion with the toggle off, the operator may, if he so desires, move the toggle to on with his thumb while performing the locking rotation, and similarly the toggle may automatically be brought to the off position by the very act of providing the counter-clockwise unlocking rotation required.

Again, if the plug is merely inserted into the receptacle when the toggle is in the off position, the very act of moving the toggle to the on position will twist the plug into the desired locked relationship with the receptacle.

Ready visibility of the circuit breaker toggle is afforded at all times.

It is not uncommon in this art to have receptacles of varying capacities, for example, 2,000; 4,000; 6,000 and 8,000 watts. The loads are, of course, varied and it is desirable to ensure that a 4,000 watt load not be inserted in a 2,000 watt receptacle. This invention provides a means for guarding against this.

It will be noted that the cut-out portion 8 occupies less than one quadrant of the plug bearing face 7. Four mutually perpendicular positions of the keyway with respect to the circuit breaker are possible, and one position might be used for each of four rated capacities. Four relative positions of lug 5 and cut-out portion 8 of the plugs are then possible-one for each maximum load connected to such plug to ensure that even with the toggle off, a 2,000 watt plug can be inserted only into a 2,000 watt receptacle, and so on.

I have described above several embodiments of my invention in detail. It will be appreciated, however, that such embodiments are offered by way of example only and should not be construed as a limitation of the scope of the invention. Such embodiments of the invention as come within the purview of the appended claims are to be considered as within the scope of this invention.

What I claim as my invention is:

1. An electrical connecting assembly comprising a receptacle having a keyway on its inner periphery and a chamber at its inner extremity, a connecting plug having a bayonet portion adapted for insertion into the receptacle and a key projecting from the outer periphery thereof, said key being adapted to slide only in the keyway, and, only after said plug has been fully inserted and upon rotation of the plug, being adapted to rotate into said chamber, said rotation being limited by the dimensions of said chamber, a bearing plate on said plug adapted to bear against a surface into which the receptacle is positioned, a circuit breaker having a toggle projecting from said surface and mounted in proximity to the receptacle, said bearing face have a cut-out portion, the dimensions of the bearing plate, and the position and dimensions of the cut-out portion being such as to permit full contact making insertion of the plug into the receptacle only when said toggle is in the off position, but to permit said toggle to be freely operated from off to on position after the plug has been inserted and the key rotated into said chamber.

2. An electrical connecting assembly as claimed in claim 1 wherein said cut-out portion occupies not more than one quadrant of said bearing plate.

3. An electrical connecting assembly as claimed in claim 1 wherein the circuit breaker is mounted beside said receptacle and in proximity thereto.

References Cited in the file of this patent UNITED STATES PATENTS 1,014,108 Wild Jan. 9, 1912 1,588,120 Maijgren June 8, 1926 2,122,058 Grant June 28, 1938 2,665,341 Wilson Jan. 5, 1954 

